1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) mobile communications system, and in particular to a CDMA mobile telephone having a function of determining whether the CDMA mobile telephone is moving.
2. Description of the Related Art
There is a growing awareness of dangers that a driver takes a mobile telephone while driving a car or is surprised with a sudden beep. To avoid such a dangerous situation, there have been proposed several mobile telephones having an automatic drive-mode setting function.
In Japanese Patent Application Unexamined Publication No. 11-234756, for example, a mobile telephone Is provided with a received signal level detector and a fading decision section, which are used to detect a period of fading occurrence. When the detected fading period is smaller than a predetermined time period, a controller determines that the mobile telephone is on the move and sets the mobile telephone to an automatic answering mode in which, when an incoming call occurs, a response message is automatically sent to the caller without starting a ringer.
In the field of CDMA mobile communications, there has been disclosed a velocity detecting method using a Doppler frequency calculated based on variations in received signal level or widened frequency band due to fading (see Japanese Patent Application Unexamined Publication No. 11-98071). To calculate the Doppler frequency, a CDMA mobile terminal is provided with a circuit for counting the number of times a received signal level has changed across an average level or a circuit for measuring the amount of widened frequency band.
However, a conventional mobile station needs an extra circuit for detecting fading occurrence, variations in received signal level, or the amount of widened frequency band, resulting in increased amount of hardware.